1. Field of the Invention
The present invention relates generally to golf balls, and more specifically, to a method of making a golf ball with a multi-layer cover. In particular, the present invention relates to a method of making a golf ball having a cover with three layers comprised of at least two different materials.
2. Description of the Related Art
Conventional golf balls typically include at least a core and a cover, and can be divided into three general types or groups: (1) two piece balls, (2) wound balls (also know as three piece balls), and (3) multilayer balls. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Balls having a two piece construction are generally most popular with the recreational golfer because they provide a very durable ball while also providing maximum distance. Two piece balls are made with a single solid core, usually formed of a crosslinked rubber, which is encased by a cover material. Typically, the solid core is made of polybutadiene that is chemically crosslinked with zinc diacrylate and/or similar crosslinking agents. The cover comprises tough, cut-proof blends of one or more materials known as ionomers such as SURLYNs®, which are resins sold commercially by E.I. DuPont de Nemours and Co. of Wilmington, Del. and IOTEK® from Exxon Corporation of Houston, Tex.
The combination of the above-described core and cover materials provides a “hard” covered ball that is resistant to cutting and other damage caused by striking the ball with a golf club. Further, such a combination imparts a high initial velocity to the ball which results in increased distance. Due to their hardness however, these balls have a relatively low spin rate, which makes them difficult to control, particularly on shorter approach shots. Thus, these types of balls are generally considered to be “distance” balls. Because these materials are very rigid, many two piece balls have a hard “feel” when struck with a club. Softer cover materials such as balata and softer ionomers in some instances, have been employed in two piece construction balls in order to provide improved “feel” and increased spin rates.
Wound balls typically have either a solid rubber- or liquid-filled center around which many yards of a stretched elastic thread or yarn are wound to form a core. The wound core is then covered with a durable cover material, such as a SURLYN® or similar material or a softer cover such as balata or polyurethane. Wound balls are generally softer than two piece balls and provide more spin, which enables a skilled golfer to have more control over the ball's flight and final position. In particular, it is desirable that a golfer be able to impart back spin to a golf ball for purposes of controlling its flight and controlling the action of the ball upon landing on the ground. For example, substantial back spin will make the ball stop once it strikes the landing surface instead of bounding forward. The ability to impart back spin onto a golf ball is related to the extent to which the golf ball cover deforms when it is struck with a golf club. Because wound balls are traditionally more deformable than conventional two piece balls, it is easier to impart spin to wound balls. However, wound higher spinning balls typically travel a shorter distance when struck as compared to a two piece ball. Moreover, as a result of their more complex structure, wound balls generally require a longer time to manufacture and are more expensive to produce than a two piece ball.
The United States Golf Association (USGA) has instituted a rule that prohibits the competitive use in any USGA sanctioned event of a golf ball that can achieve an initial velocity of greater than 76.2 meters per second (m/s), or 250 feet per second (ft/s), when struck by a driver with a velocity of 39.6 m/s, i.e., 30 ft/s (referred to hereinafter as “the USGA test”). However, an allowed tolerance of two percent permits manufacturers to produce golf balls that achieve an initial velocity of 77.7 m/s (255 ft/s).
Regardless of the form of the ball, players generally seek a golf ball that delivers maximum distance, which requires a high initial velocity upon impact. Therefore, in an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls with initial velocities in the USGA test that approximate the USGA maximum of 77.7 m/s or 255 35 ft/s as closely as possible.
Therefore, golf ball manufacturers are continually searching for new ways in which to provide golf balls that deliver the maximum performance in terms of both distance and spin rate for golfers of all skill levels.
Typically, the golf ball cover layer is formed by one of two processes. The first process includes the compression molding of hemispheres. First, two hemispherical covers, called half shells, are injection molded. The hemispheres are then placed around a core and compression molded so that they fuse around the core and so that dimples are imparted into the cover. The cover is then finished to remove any visible molding lines or residue. The second process, called the retractable pin injection molding process, involves injection molding the cover directly around a core positioned on pins, retracting the pins once the cover material sufficiently surrounds the core, removing the covered core, and finishing it to form a completed golf ball. In both cover forming processes, the injection molding of the covers involves techniques known in the art. These techniques generally involve forcing melted material to substantially fill and take the shape of a mold, thereby forming a cover or hemisphere. When the material is cool enough to substantially maintain the shape of the mold, it is ejected from the mold, or demolded.
Typically, the cover material begins the injection molding process as resin pellets which are stored in a hopper. The pellets are gravity fed into a heated cylinder which melts the pellets as a screw pushes the softening pellets toward an accumulation zone. When enough melted material is accumulated to fill the mold, the screw is pushed or stroked forward, thereby forcing the melted material into the mold. Many prior art references are directed to mixing different materials to form new cover materials. This is traditionally accomplished by mixing pellets of different materials in the injection mold hopper.
Relatively recently, a number of golf ball manufacturers have introduced multilayer golf balls, i.e., having multiple core intermediate mantle and/or cover layers, in an effort to overcome some of the undesirable aspects of conventional two piece balls (such as their hard feel) while maintaining the positive attributes of these golf balls (including their increased initial velocity and distance). Further, it is desirable that such multilayer balls have a “click and feel” as well as spin characteristics approaching that of wound balls.
Manufacturers generally provide the golf ball with a durable cover material, such as an ionomer resin, or a softer cover material, such as polyurethane. Chemically, ionomer resins are a copolymer of an olefin and an α,β-ethylenically-unsaturated carboxylic acid having 10-90% of the carboxylic acid groups neutralized by a metal ion and are distinguished by the type of metal ion, the amount of acid, and the degree of neutralization. Commercially available ionomer resins include copolymers of ethylene and methacrylic or acrylic acid neutralized with metal salts. Examples include SURLYN® and IOTEK®.
Surrounding the core with an ionomeric cover material provides a ball that is virtually indestructible by golfers. The core/cover combination permits golfers to impart a high initial velocity to the ball that results in improved distance.
Polyurethanes are used in a wide variety of applications including adhesives, sealants, coatings, fibers, injection molding components, thermoplastic parts, elastomers, and both rigid and flexible foams. Polyurethane can be produced by the product of a reaction between a polyurethane prepolymer and a curing agent. The polyurethane prepolymer is generally a product formed by a reaction between a polyol and a diusocyanate. The curing agents used previously are typically diamines or glycols. A catalyst is often employed to promote the reaction between the curing agent and the polyurethane prepolymer.
Since about 1960, various companies have investigated the usefulness of polyurethane as a golf ball cover material. U.S. Pat. No. 4,123,061 teaches a golf ball made from a polyurethane prepolymer of polyether and a curing agent, such as a trifunctional polyol, a tetrafunctional polyol, or a fast-reacting diamine. U.S. Pat. No. 5,334,673 discloses the use of two categories of polyurethane available on the market, i.e., thermoset and thermoplastic polyurethanes, for forming golf ball covers and, in particular, thermoset polyurethane covered golf balls made from a composition of polyurethane prepolymer and a slow-reacting amine curing agent, and/or a difunctional glycol.
Additionally, U.S. Pat. No. 3,989,568 discloses a three-component system employing either one or two polyurethane prepolymers and one or two polyol or fast-reacting diamine curing agents. The reactants chosen for the system must have different rates of reactions within two or more competing reactions.
The color instability caused by both thermo-oxidative degradation and photodegradation typically results in a “yellowing” or “browning” of the polyurethane layer, an undesirable characteristic for urethane compositions are to be used in the covers of golf balls, which are generally white.
U.S. Pat. No. 5,692,974 discloses golf balls which have covers and cores and which incorporate urethane ionomers. The polyurethane golf ball cover has improved resiliency and initial velocity through the addition of an alkylating agent such as t-butyl chloride to induce ionic interactions in the polyurethane and thereby produce cationic type ionomers. UV stabilizers, antioxidants, and light stabilizers may be added to the cover composition.
U.S. Pat. No. 5,484,870 discloses a golf ball cover comprised of a polyurea. Polyureas are formed from reacting a diisocyanate with an amine.
U.S. Pat. No. 5,823,890 discloses a golf ball formed of a cover having an inner and an outer cover layer compression molded over a core. The inner and outer cover layers should have a color difference ΔE in Lab color space of up to 3.
U.S. Pat. No. 5,840,788 discloses a UV light resistant, visibly transparent, urethane golf ball topcoat composition for use with UV curable inks. The topcoat includes an optical brightener that absorbs at least some UV light at wavelengths greater than about 350 nm, and emits visible light, and a stabilizer package. The light stabilizer package includes at least one UV light absorber and, optionally, at least one light stabilizer, such as a HALS.
U.S. Pat. No. 5,494,291 to Kennedy discloses a golf ball having a fluorescent cover and a UV light blocking, visibly transparent topcoat. The cover contains a fluorescent material that absorbs at least some UV light at wavelengths greater than 320 nm and emits visible light.
Colored golf balls have been produced for many years. In the 1960s Spalding produced a yellow range ball with a blended cover that included polyurethane.
U.S. Pat. No. 4,798,386 makes reference to white cores and clear covers and even locating decoration on the core to be visible through the clear cover. This concept requires a core which has a satisfactory hue to achieve the desired finished ball coloration. A polybutadiene rubber core of such a color has never been produced and as such, clear cover 2-pc ball have had limited market success.
U.S. Pat. No. 4,998,734 describes a golf ball with a core, a clear cover and “layer interdisposed therebetween.” However, the intermediate layer described is a thin layer of paper or plastic material whose purpose is only to bear textural, alphanumeric or graphical indicia. Meyer teaches that the layer should be sufficiently thin to permit substantial transference of impact forces from the cover to the core without substantially reducing the force.
The Pro Keds “Crystal π” golf ball appeared in the Japanese market. It had a white core bearing the ball markings and a clear Surlyn cover. This ball had a very thick clear cover (>0.065″) and the surface dimple coverage was very low.
In the early 1990s, Acushnet made clear Surlyn cover, two piece Pinnacle Practice balls. The covers were 0.050″ thick.
A prototype Wilson Surlyn covered two piece ball, “Quantum”, of a design similar to the Pro Keds ball was found in the US in the late 1990s. The cover was greater than 0.065 inches thick.
U.S. Pat. No. 5,442,680 is directed to a golf ball with a clear ionomer cover. The patent requires a blend of ionomers with different cations.
In the early 1990s, a solid one piece urethane golf ball having a hole for the insertion of a chemi-luminescent tube was sold as a “Night Golf” ball. It was relatively translucent to create the glow, but it was far from having the performance characteristics of standard golf balls.
Two piece balls have been sold under the tradename “Glow Owl” which utilize a white core and a cover with glow in the dark materials. This ball is believed to embody the technology described in U.S. Pat. No. 5,989,135, which describes a “partially translucent” cover.
At the January 2001 PGA Show, Wilson displayed samples of “iWound” golf balls with clear covers. They were not balls for actual play but mock-ups used to display their new “lattice wound” technology. The lattice (discontinuous inner cover layer) was Hytrel and the Surlyn outer cover layer was clear. Both the Hytrel lattice and red core were visible through the clear cover. No markings were on the core or lattice.
To date, it has been difficult for manufacturers to properly attain the desired long-term appearance of polyurethane compositions used in golf ball covers without adversely affecting golf ball performance. Many golf balls have at least one layer of “paint” covering the cover material. This long-felt problem in the golf ball art has now led the Applicants to seek a desirable formulation of a polyurethane composition suitable for use in golf ball covers that exhibits improved properties and allows for substantially different looking golf balls
There are a number of multilayer ball patents directed towards improving the spin, click or feel of solid balls while maintaining the distance provided by the solid construction. A variety of approaches to manipulating the core construction are described in the art. For example, U.S. Pat. No. 5,072,944 discloses a three piece solid golf ball having a center and outer layer which are prepared from a rubber composition, preferably having a base rubber of polybutadiene. This patent teaches that it is desirable that the center core is softer than the outer layer, wherein the layers have a hardness (Shore C) of 25-50 and 70-90, respectively.
U.S. Pat. No. 4,625,964 relates to a solid golf ball having a polybutadiene rubber core of a diameter not more than 32 mm, and a polybutadiene rubber intermediate layer having a specific gravity lower than that of the core material.
U.S. Pat. No. 4,848,770 discloses a non-wound three piece golf ball which includes a core of a highly filled synthetic rubber or polymeric material, an intermediate mantle of an unfilled synthetic rubber, and a cover. The core and intermediate mantle have a hardness between 50-95.
U.S. Pat. No. 5,002,281 is directed towards a three piece solid golf ball which has an inner core having a hardness of 25-70 (Shore C) and an outer shell having a hardness of 80-95 (Shore C), wherein the specific gravity of the inner core must be greater than 1.0, but less than or equal to that of the outer shell, which must be less than 1.3.
U.S. Pat. No. 5,253,871 concerns a golf ball having a three piece structure comprising an elastomer core, an intermediate layer of a thermoplastic material containing at least 10% of ether block copolymer, preferably blended with an ionomer and a thermoplastic cover.
U.S. Pat. No. 4,431,193 relates to a golf ball having a multilayer cover wherein the inner layer is a hard, high flexural modulus ionomer resin and the outer layer is a soft, low flexural modulus ionomer resin, wherein either or both layers may comprise a foamed ionomer resin.
U.S. Pat. No. 5,314,187 also relates to golf balls having a cover formed with multiple layers, wherein the outer layer is molded over the inner layer and comprises a blend of balata and an elastomer and the inner layer is an ionomer resin.
U.S. Pat. No. 4,919,434 is directed towards a golf ball having a cover which comprises an inner layer and an outer layer each of which comprise a thermoplastic resin, preferably the layers comprise materials that are capable of fusion bonding with each other.
UK Patent Application Nos. GB 2,291,817 and 2,291,812 are both directed toward a wound golf ball with improved distance comprising a dual cover layer, wherein the inner cover layer has a high hardness as compared to the outer cover layer. These references teach that the cover layers may be formed from balata or ionomer resins and should have a combined thickness of less than 4 mm.
UK Patent Application No. GB 2,278,609 discloses a multilayer golf ball providing enhanced distance without sacrificing playability or durability comprising a core, an inner cover layer and an outer cover layer wherein the inner cover layer comprises a high acid ionomer and the outer cover layer comprises a soft ionomer or a non-ionomeric thermoplastic elastomer.
Methods of manufacturing multilayer articles such as automobile headlights in a substantially different manner are discussed in U.S. Pat. Nos. 4,944,909 and 4,670,199 as well as in German Patent No. 4041799. Each of these references disclose injecting two materials through a single injection sprue or channel. The basic method is comprised of the steps of injecting a first material through a sprue into the mold and then injecting a second material into the mold through the same sprue. Due to the flow characteristics of the molten material, the first material adheres to the mold to form an outer skin and the inner material tends to flow through the center of the skin layer such that the second material is sandwiched between the first material.
Multilayer golf balls can be formed using a variety of constructions. For example, multilayer balls may have two or more cover layers molded around a conventional core with one or more intermediate layers interposed between the cover and the core. Likewise. multilayer balls may be formed from cores having more than one core layer and may optionally contain one or more intermediate and/or cover layers. Multilayer balls may even comprise a conventional wound core around which at least one intermediate layer and/or at least one cover layer is formed. Examples of multilayer balls include the Altus Newing (Bridgestone), Reygrande 2×2 (Bridgestone), Giga (Spalding), Metal Mix (Dunlop), and Ultra Tour Balata (Wilson).